1. Field of the Invention
The present invention relates to a method of and apparatus for nondestructively determining the dimensional changes in an object as a function of temperature and, in particular, relates to an method of and apparatus for developing a dilatometry model of an object to be manufactured, wherein the model can be used by an automated quality control system to more accurately determine the dimensional quality of an object at ambient temperatures, based on a dimensional analysis of the object conducted at elevated temperatures by means of penetrating radiation and computer models of the object being examined.
2. Description of Prior Art
Historically, various means have been used to provide quality control of objects during their manufacture. In many manufacturing environments where the product being manufactured, such as tube or pipe, is actually formed at elevated temperatures, it is often desirable to initially test the product when the product is at an elevated temperature, otherwise a significant number of out-of-specification products can be produced before a defect is discovered.
In more recent manufacturing process control environments, the ability to test the product-in-manufacture at elevated temperatures is especially important if control signals are to be feedforward to additional production processes, which can correct the defect while the product remains at elevated temperatures.
In the past, quality control systems have taken measurements at elevated temperatures for the purpose of controlling the quality of the product's dimensions. For example, U.S. Pat. Nos. 3,841,123 and 3,851,509 contemplate taking temperature measurements of sheet metal as its thickness is measured by force gauges and a final X-ray gauge in order to control the manufacturing process. Likewise, U.S. Pat. No. 3,592,031 discloses an apparatus and method for correcting the manufacturing process if a measured temperature is different than the expected temperature. Finally, U.S. Pat. No. 3,248,916 contemplates another sheet metal production process control system that limits roller pressures based upon a temperature measurement.
All of the prior art systems above disclose systems that do not continuously measure the same cross-section of the object over a range of temperatures. Rather all of the disclosed inventions assume the existence of previously developed dilatometry data. Moreover, the gamma ray gauges used in the prior art devices are only accurate for measuring thickness if the density of the material is known. Since the density of the material changes with the temperature, and although the density may be calculated if the precise chemical composition of the material is known, these gauges are not useful for collecting accurate dilatometry data. Additionally, the above prior art systems only measure a single dimensional parameter of simple objects--its thickness while the present invention measures multiple parameters of complex geometrically regular objects.
Historically, dilatometry curves and data were developed for materials of a known chemical composition by various traditional techniques, such as measuring a single dimension of an object with strain gauges, laser interferometer, or other techniques as the object cooled. More recently, laser interferometers have been used to measure the change in dimensions of a sample of a product of a known chemical composition as the material cooled. This empirically developed dilatometry data, however, was limited in several respects. First, the dilatometry data for a particular product to be manufactured is usually based on empirical data developed from a sample of known chemical composition prior to the actual production run. It was impractical to sample each batch of material made in order to generate a dilatometry curve specific to each batch of material using the old measuring techniques. Secondly, it would be impractical to test these samples in an industrial environment since the prior art test requires the sample be placed in a chamber filed with inert gas. Thirdly, the prior art methods only measured one dimension of a sample at a time. The present invention measures the entire cross-sectional shape of a sample. Finally, the present invention is capable of taking measurements of a full size object at actual cooling rates and on line in real production cooling environments.